Denmark's Novo Nordisk has been sued by a group of healthcare purchasing companies in the United States for allegedly wrongfully keeping generic copies of its Prandin diabetes drug off the market. A spokesman for Novo said on Tuesday the company aimed to get the case dismissed, but had no further comment. In 2005 Caraco Pharmaceutical Laboratories, a subsidiary of Indian drug maker Sun Pharmaceutical Industries, applied to get a generic version of Prandin approved by 2009, when Novo's patent on the drug would expire.